Free piston and cylinder assembly for hydraulic pumps and motors



March 25, 1969 R. R. GOODWIN 3,434,429 FREE PISTON A ND CYLINDER ASSEMBLY FOR HYDRAULIC PUMPS AND MOTORS Filed March 14, 1967 fi/Cf/AAD R. 60 00W/A/ INVENTOR.

3 771 5 4 BY gag M9 ATTORNEYS y? 4, wafim, 466W? United States Patent O U.S. Cl. 103-162 1 Claim ABSTRACT OF THE DISCLOSURE A fluid pump or motor having rotatable cylinder blocks joined together by a constant velocity joint. The cylinders in said rotatable cylinder blocks are positioned opposite one another and are acted upon by spherical pistons fixed upon common, nonflexible piston rods, through which a passage is bored for passage of the working fluid during rotation of the heads.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

In current designs of positive displacement pumps of the axle piston type, it has been found necessary to provide ball sockets, slippers, wristpins, and other connecting devices to transfer forces. Such apparatus has proved expensive to manufacture and requires frequent repair.

It has been found in many of the prior art fluid pumps and motors, that excessive friction occurs at the points of connection and great difliculty has arisen due to inefficiency in providing lubrication and cooling at these points of connection.

It is also found in some designs that the distortion of the pistons occurs causing additional frction and resultant heat build up.

In many cases, scufling of the piston and cylinder walls occurs due to the binding of the piston and its piston rod, or due to dirt, thermal shock, etc.

It is therefore an object of the present invention to obviate each and every one of the above described disadvantages currently occurring in the prior art.

It is also an object of the present invention to reduce or eliminate friction normally encountered at the point where the piston is connected to the piston rod and where it comes in contact with the revolving cylinder block or swash plate.

It is also an object of the present invention to provide an hydraulic pump or motor in which the cooling and lubrication of parts at their point of greatest friction is improved by increasing the fluid flow.

It is a further object of the present invention to provide an hydraulic pump or motor in which the bending moments encountered in conventional piston designs are entirely eliminated.

It is also an object of the present invention to provide an hydraulic pump or motor in which the scufling of piston and cylinder is completely eliminated.

The above and further objects of the invention will become obvious to those skilled in the art upon reading the following description of the preferred embodiment of the invention which is furnished for illustration and not for limitation.

In the drawings:

FIGURE 1 shows a sectional view of opposing cylinder blocks of a preferred embodiment of the hydraulic pump or motor.

FIGURE 2 shows a view of one cylinder block of the preferred embodiment of the hydraulic pump or motor 3,434,429 Patented Mar. 25, 1969 with specific attention being given to the bores of said cylinder block.

It will be understood that although the description describes an hydraulic pump, those skilled in the art will obviously be aware of the usage of such structure as an hydraulic motor.

Now more specifically, in FIG. 1, the numeral 11 generally designates an hydraulic pump of the preferred embodiment of the invention. Power is provided to the pump by means of a shaft 13, which is welded or otherwise suitably connected to a revolvable cylinder block 15. As can be seen in FIGURE 2, cylinder block 15 has, suitably spaced therein, cylinders 17. In the center of cylinder 15, a suitable aperture 19 is bored, and slots 21 are machined at the periphery of said aperture for a purpose to be later described.

Referring once again to FIGURE 1, a second revolvable cylinder block 23 contains cylinders 25, a central aperture 31, and slots 33. The cylinder block 23 is very similar to block 15 as shown in FIGURE 2. At the base of each cylinder 25, apertures 27 allow the passage of fluid to the cylinders from a fluid source. A valve plate 35 is suitably mounted on cylinder block 23 and is spaced therefrom by a bushing 37. Suitable ports in the shapes of curvilinear slots 39, are machined in the valve plate 35, so as to cooperate with fluid apertures 27, in cylinder block 23. The cooperation of the slots 39 with the fluid aperture 27 is well known by those skilled in the art.

Situated between cylinder blocks 15 and 23 is a piston centering disk 41. The piston centering disk is mounted on universal timing shaft 43 having teeth 45 at the ends there-of. Shaft 43 enters apertures 19 and 31 in cylinder blocks 15 and 23, respectively. The teeth 45, thereon, cooperate with slots 21 and 33, machined into the periphery of the apertures 19 and 31. Thus, when power is sup plied to shaft 13, thereby causing the revolution of cylinder block 15, cylinder block 23 is also revolved due to the cooperation of universal timing shaft 43 with apertures 19 and 31 and the slots therein. Suitably mounted on piston centering disk 41 are unitary, or nonflexible, piston rods 47 which are positioned :so as to cooperate with opposed cylinders 17 and 25 in the two cylinder blocks. A spherical piston head 49 is machined onto each end of each piston rod 47, and piston rings 51 are suitably installed in each piston head. An oil passage 53 extends from the top of one spherical piston 49, through piston shaft 47, to the top of the opposite piston 49. This passage provides for the flow of working fluid from one cylinder 25 to the opposite cylinder 17.

In the operation of the device, when power is applied to shaft 13 so as to cause it to rotate in either direction, the piston couple, at the bottom of FIGURE 1, is rotated to a position shown in the top of FIGURE 1 during the first of revolution. In doing so, the piston heads 49 move away from the tops of cylinders 17 and 25. Any fluid that is present at the ports 39 of valve plate 35, then tends to move in and fill the cylinders. Fluid enters cylinder 17 by means of fluid passage 53 in piston shaft 47. During the second 180 of revolution, that is, from top to bottom as shown in FIGURE 1, the pistons move into the cavities or approach the top of cylinders 17 and 25, thereby forcing the fluid out so that it can be directed to the place where it is ultimately used by means of passage through the lower port 39* in valve plate 35. As shaft 13 continues to rotate, the working fluid is continuously drawn into the cylinders and then removed therefrom in the above described manner. The shaft 43 keeps the two cylinder blocks in synchronization.

It will thus be noted that the applicant has herein provided a new and novel hydraulic motor or pump,

wherein the pistons are ground with a spherical configuration so that there will be no binding in the cylinder bores. The disk 41 is used to keep the pistons in a centered position. The same could be accomplished of course 'by designing, into each piston area, centering springs, snap rings, etc.

This invention has therefore shown a means to replace the common ball and socket, slippers, or wristpin type of connection between the piston and the piston rod and the rod and the swashplate with a ball piston Because of the flow of Working fluid through the piston and rod assembly and in and around the piston itself on either end, cooling is enhanced and friction is reduced.

Wherein I claim:

1. A hydraulic positive displacement apparatus of the axial piston type comprising opposed first and second cylinder blocks positioned on an offset axis, a universal timing shaft connected between said cylinder blocks by means of a universal joint at each end of said shaft, each said universal joint disposed respectively at the center of each said first and second block to ensure said blocks rotate in unison, a plurality of cylinders in each said first and second block, each said cylinder having a substantially dome-shaped bottom wall, disk means mounted on said shaft and positioned normal thereto fixedly carrying a plurality of longitudinal unitary piston rods thereon, each of said piston rods retained by said disk means in substantially parallel relationship with said shaft whereby each said rod extends into one cylinder in each of said first and second blocks, a spherical piston integral with and positioned on each end of each of said piston rods for cooperation with said cylinders, each said spherical piston conformin to the dome-shaped bottom Wall of its associated cylinder, port means in said first block communicating with each of the cylinders therein, valve plate means having slots therein mounted on said first block for movement relative thereto whereby the valve slots cooperate with the cylinder ports to allow hydraulic working fluid to be continuously drawn into and out of said first block cylinder port means, shaft means fixedly mounted on said second block to allow a turning force to be transmitted thereby, a passage extending axially through each of said piston rods and its associated spherical pistons such that each of said passages allows flow of the hydraulic Working fluid to transfer to and from the cylinders in said second block to the cylinders in said first block in response to the revolving movement of said blocks.

References Cited UNITED STATES PATENTS 2,556,585 6/1951 Jarvinen 123-43 2,146,133 2/1939 Tweedale 103-162 2,821,932 2/1958 Lucien 103173 2,875,701 3/1959 Ebert 103162 2,956,845 10/1960 Wahlmark 103-162 3,180,275 4/1965 Boulet 103l62 3,196,801 7/1965 Ifield 103162 3,289,604 12/1966 Wahlmark 103-162 FOREIGN PATENTS 24,941 3/1906 Great Britain.

WILLIAM L. FREEH, Primary Examiner.

US. Cl. X.R. 

